The present invention relates to a new and improved method for remote control through a power supply system, and to an arrangement or apparatus for carrying out this method.
Various methods for remote control through a power supply system are already known in the art. One of the more widely used techniques is, for example, the technique known as ripple control in which a transmitter, preferably installed at a substation of an energy-supply network, superimposes control commands in the form of alternating-current signals or pulse sequences upon an associated power supply system. These control commands can be selectively received at any point of the power supply system by receivers connected to the power supply system. Ripple-control or remote control systems of this type can be used to switch certain groups of current consumers, such as boilers, street-lighting systems etc., on or off by remote control. Ripple-control systems of this kind also can be used for transmitting special-purpose commands, for example for fire fighting or air-warning purposes and so forth.
Although ripple-control techniques of the nature referred to above have generally proved to be satisfactory, considerable difficulties occasionally arise due to the fact that the control commands superimposed upon a power supply system not only spread out or propagate in a forward direction, i.e. in the direction of energy flow to the consumers associated with the particular substation, they also spill over backwards through feed transformers at the particular substation into a higher-order high-voltage network and, through this higher-order high-voltage network and through further feed transformers, pass undesirably into a power supply system associated with a neighboring substation. This fault occurs especially in cases where relatively low transmitting frequencies, for example in the order of 300 c/s, are used, because the aforementioned feed transformers in the substations only exhibit relatively low damping for frequencies as low as these. In view of the fact that the higher-order power supply system which represents the interfering transmission path, has a voltage of, for example, 50 KV or more and is designed for high outputs, it is obvious that frequency-selective blocking means become extremely expensive and also represent undesirable elements in terms of the operational reliability of power supply systems. In the absence of such blocking means, however, ripple-control or remote control receivers in an adjacent network would be in danger of responding falsely to control commands foreign to that network on account of this undesirable signal spillover into an adjacent power supply system.